Treatment of limestone



July 1l, l939. T. C. TAYLER I 2,165,735

l TREATMENT 0F LIMEsToNE Filed June 4, 1937 Chf- /N VENTO/e )Zero/9 Cfoy/er- A TTORNE V Patented .my 11, 193e UNITED STATES PATENT olf-FICE 4Claims.

This invention relates to processes for the treatment of limestone toproduce lime therefrom; and is more particularly concerned with a methodand means for pretreating limestone before it is introduced into aburning kiln.

It is a primary object of .this invention to provide a method forpretreating limestone whereby the normal capacity of a continuous rotarykiln operating on such pretreated stone is substan- V1o uany increased.

It is among the objects of this invention to provide a novel apparatusfor carrying o ut the hereinafter described lprocess for thepretreatment of limestone.

Another object of the invention is to provide means wherein .limestonecan be pretreated wherein unusual heat economy is obtained.

To the accomplishment of the foregoing and related ends the invention,then, comprises the zo method and means hereinafter fully described land particularly pointed out in the claims, the

annexed drawing, and the following description,

setting forth in detail one mode and means for carrying out theinvention, such disclosed mode and means illustrating, however, but oneof the various'ways inwhich the principle of the invention may be used.

1n said annexed drawing, the single figure shows a side elevation,partly in section, of a preferred form of my apparatus wherein the' Thegas employed to heat the raw stone mayA be derived from any suitablesource and should be supplied at a temperature above about 1000 F., andpreferably about1200f-1000 F., to yield the best results.. I have foundthat in commercial practice substantially all ofthe sensible heat in theexhaust gas from a rotary lime-burning kiln can be recovered and'utilized where such gas is fed into the raw stone in the pretreatingapparatus 'at a temperature of approximately 1400"V The rate of ow ofstone through the heat exchange zone can be so controlled that the`stone attains a temperature only slightly below that of the incoming hotgas, e. g. a diiIerential of about 25-100 F. From the heat exchange zonethe heated stonev is fed into a zone insulated to prevent heat loss,wherein it is allowed to remain for a suitable period of time, e. g.about one to two hours. From this soaking zone the stone, preferablywhile still hot, is led into the usual burning kiln, preferably of therotary type. The hot stone may advantageously be introduced into theburning kiln through the hot gas leaving the same.

, Referring now to thev drawing:

In the single figure, a storage bin l for raw limestone is provided atthe bottom thereof with an loutlet pipe 2 whichdepends into anadjustable telescoping spout 3. Said spout 3 is mounted to slidevertically in a cover plate 4 which closes the top of a cylinder 5constituting the upper part of the treating chamber 6. The upper part ofthe treating chamber B'is provided with an oiftake pipe 'I through thecover plate 4, leading to a fan 8 for exhausting the gases from saidchamber 6. The lower part of the chamber 6 consists essentially of aninverted conical hopper 9 provided at the bottom thereof with an voutletfor treated stone, and means to control the rate of withdrawal of stonefrom the chamber l. Suitable means for such purpose is here showndiagrammatically as a vibrating conveyor I0.

The'cylinder 5 andthe inverted cone '9 have a common vertical axis, butare arranged' so that the bottom of the cylinder is slightly above thebase of the cone, andthe diameter of the cylinder is somewhat less thanthe diameter of the base of the cone, thereby providing an annularopening I i in said chamber 6 wherethrough the heating gas is admittedto the chamber,- The relationship between the diameterof the cylinder 5,the diameter of the base of the inverted cone 9, and the verticaldistance between the bottom of the cylinder and the cone base should besuch that stone travelling downwardly through the chamber will not spillover the rim of the cone base, and'ls determined by the angle of ow .ofcrushed` limestone, which is, approximately 30.i0. -Y

A suitable distributing element, here illustrated as` a cone I2, havinga common vertical axis with that of the aforesaid cylinder 5 andinverted cone l, is placed within said chamber-l to distribute thegravitational ilow of limestone therethrough and to provide means toobtain more .annular inletl Il thereto.

the heating gases, to prevent substantial loss of heat, and to confinethe hot gases so that they can only ow into the chamber 6 through theSaid gas inlet path I4 may lead from the gas discharge end of a continuous rotary kiln I5 and may contain a part of the conveying means I6for feeding the pretreated stonev from the treating chamber 6 to thekilny l5.l

To illustrate the practice of my invention in the typ'e of apparatusjust described, the following example is given:

Raw limestone, sized to pass through a one and one-quarter inch screenand`be retained on a flve-eighths inch screen, was fed at asubstantially uniform rate from a storage bin into'a treating chamberconstituting a gas-stone contact zohe and a soaking zone. 'I'he exhaustgases from a rotary kiln were led into the chamber at a tem- Derature ofabout 14:00o F. 'I'he kiln wherefrom such gases were obtained was anordinary rotary lime burning kiln, having an internal diameter f of sixfeet and a length of approximately one hundred feet, the-normal ratedcapacity of such kiln being forty. tons per day of finished lime.

The temperature of the treated stone withdrawn from the chamber at thebottom of the soaking zone was approximately 1300 F. 'I'he gasesexhausted from the top of the treating chamber had a temperature ofapproximately 300 F. The treated stone withdrawn from the bottom of saidsoaking zone was continuously conveyed intothe rotary kiln, and auniformly burned lime product obtained at the dischargey end of thekiln. Approximately '15 tons per day of uniformly burned lime wasobtained under the operating conditions described.

My process provides a way of pretreating limestone which utilizes theheat in the exhaust-gases from rotary kilns, thereby lending to limeburning operations a high over-all eiliciency; produces a uniformproduct by avoiding the simultaneous overand under-burning of stonewhichis experienced in most rotary kilns; and substantially increases thenormal capacity of rotary limeburning kilns. g

Other modes and means of applying the principle of my invention may beemployed instead of those explained, change being made as regards thesteps or apparatus herein disclosed, provided the steps or means statedby any of the following Aclaims or the equivalent of any such statedsteps which consist in feeding ,the stone into a zone wherein it isintermingled with hot gas to transfer heat from said gas to said stone,then into a zone out of contact with said gas and permitting said stoneto so k in said zone, and thereafter introducing th' A stone from saidsecond zone into a burning kiln.

2f In a method of treating limestone to prepare the same for burning ina kiln, the steps which consist in feeding the stone into a zone whereinit is intermingled with gas supplied at a temperature above about 1000F. to transfer heat from said gas to said stone, then into a zone out ofcontact with said gas and permitting said stone to soak insaid zone, andthereafter introducing the stone from said second zone into a burningkiln.

3. In a method of treating limestone to prepare the same for burning ina kiln, the steps which consist in feeding the stone into a zone whereinit is intermingled with gas supplied at a. temperature of between about1200* F. and about 1600 F. to ,transfer heat from said gas to saidstone, then into a zone out of contactwith said gas and permitting saidstone to soak in said zone,

and thereafter introducing the stone from'said second zone into aburning kiln.

4. In a method 'of treating limestone to prepare the same for burning ina kiln,the steps which consist in feeding the stone into a zone whereinit is intermingled with hot gas to transferheat from said gas to saidstone, then into a zone out of contact with said gas and permittingAsaid stone to soak in said zone. and thereafter introducing the stonewhile still at an elevated temperature from said second zone into aburning kiln.

THERON C. TAYLER.

